2020-2021

Olduvai Gorge (northern Tanzania) is one of the best known and most iconic palaeontological and archaeological sites in the world. In more than a century of research it has yielded an impressive record of fossils and stone tools which stands as a compendium of human evolution in the context of environmental changes of East Africa in the last 2 Ma. Recent field work in the DK site at Olduvai lead to the retrieval of a partial crocodile cranium nicknamed Black Sun because it was discovered during an annular solar eclipse. The specimen is here described and compared with extinct and extant African crocodylids. The new cranium can be referred to Crocodylus anthropophagus, a Pleistocene species hitherto found only in Olduvai Gorge. Thanks to the good preservation of the skull table, its morphology is here characterised for the first time. Black Sun represents to date the earliest (ca. 1.9–1.85 Ma) and the most informative cranium of C. anthropophagus in the fossil record. Our phylogenetic analysis supports a strict relationship between C. anthropophagus and Crocodylus thorbjarnarsoni, a large species from the Plio-Pleistocene of the Turkana Basin (Kenya). These two sister taxa share a combination of characters which places them at the base of Crocodylus, providing an intriguing element to the debate on the African or extra-African origin of this genus. 

Fossil footprints are very useful palaeontological tools. Their features can help to identify their makers and also to infer biological as well as behavioural information. Nearly all the hominin tracks discovered so far are attributed to species of the genus Homo. The only exception is represented by the trackways found in the late 1970s at Laetoli, which are thought to have been made by three Australopithecus afarensis individuals about 3.66 million years ago. We have unearthed and described the footprints of two more individuals at Laetoli, who were moving on the same surface, in the same direction, and probably in the same timespan as the three found in the 1970s, apparently all belonging to a single herd of bipedal hominins walking from south to north. The estimated stature of one of the new individuals (about 1.65 m) exceeds those previously published for Au. afarensis. This evidence sup- ports the existence of marked morphological variation within the species. Considering the bipedal footprints found at Laetoli as a whole, we can hypothesize that the tallest individual may have been the dominant male, the others smaller females and juveniles. Thus, considerable differences may have existed between sexes in these human ancestors, similar to modern gorillas.

Evidence from various climate proxies provides us with increasingly reliable proof that only in the past 10 millennia were natural systems more or less as we see them at the present (without considering human impact). Prior to 10,000 years ago, natural systems repeatedly changed under the influence of an unstable climate. This is particularly true over the last one million years. During these times, terrestrial environments were populated by a diversity of large animals that did not survive either the last dramatic climate change or the increasing power of humans. The volume of continental ice covering the land and its impact on the planet’s physiography and vegetation have varied consistently. We can try to imagine extreme conditions: the very cold springtimes of the full glacials, and the warm springtimes of the rapid deglaciation phases, with enormous volumes of water feeding terrifying rivers. Most of this story is frozen in the ice cover of Greenland and Antarctica, the deep layers of which have been reached by human coring activities only over the past half century. Shorter cores have been drilled in high-altitude ice caps (e.g., in the Andes) that provide insight into other parts of the planet. The interpretation of the signals locked into the ice cores led to the reconstruction of climatic curves covering approximately the past 800 millennia. In addition, long sediment cores have been recovered from thousands of lakes across the globe and yielded data useful to estimate climatic trends based on pollen records. In the past one to three million years, the continents and oceans were in roughly their present-day locations. Environmental factors, including tectonics (mountain uplift or closure of ocean gateways), interacted with the overall long-term oscillation in atmospheric carbon-dioxide concentration, which, in turn, influenced vegetation cover and ecosystem composition. Well-established glacial-interglacial cycles impacted biotic dispersal events at mid-to-high latitudes and determined the geographical restriction and expansion of tropical and subtropical (warm-temperate) biomes around the globe. This book chapter constitutes an imaginary field trip, presenting the reader with exemplary records of environments, plants, large mammals, and hominins impacted by cooling and warming phases, glaciations, changes in rainfall patterns, and sea level culminating in the world of today.